Gas-conserving regulators include oxygen regulators, which are used to supply a patient with a regulated flow of oxygen. The oxygen is supplied by a source of highly-compressed oxygen, such as from a supply tank, which has its pressure reduced to a low pressure (e.g., 22 PSI) for delivery to the patient. Typical oxygen regulators employ a back-pressure piston to supply a continuous flow of that low pressure oxygen to the patient. Much of that oxygen is wasted because it is not inhaled by the patient.
To reduce the amount of wasted oxygen, oxygen-conserving regulators have been developed. These conservers tend to limit the oxygen flow to periods of inhalation. The oxygen flow is typically controlled electronically or pneumatically. Of the pneumatic types, there are two common types of systems: single-lumen and dual-lumen.
In a typical electronic conserver, a solenoid valve controls the flow of oxygen to the patient. The solenoid valve can accurately open to provide the flow of oxygen to the patient when the patient inhales, and close between breaths. Typically, the solenoid valve has high energy requirements and is battery powered.
In typical dual lumen pneumatic conserving regulators, a reservoir coupled to the oxygen source holds a supply of oxygen for delivery to the patient. Delivery of the oxygen is controlled by a slave diaphragm that separates the reservoir from a control gas chamber. The slave diaphragm seals the opening to a delivery nozzle when the patient is not inhaling and releases the seal from the nozzle opening when the patient inhales. The slave diaphragm is made from a flexible material and is generally pressurized toward the closed position. Operation of the slave diaphragm is controlled by a pilot diaphragm, which is coupled to the patient. When the patient inhales, the pilot diaphragm lifts off an orifice pneumatically connected to the control gas chamber. The oxygen in the control gas chamber is then expelled, creating a pressure drop sufficient to allow the slave diaphragm to move away from the slave nozzle, thus allowing flow to the patient.
Dual-lumen devices use a cannula with two separate hoses for connecting to the conserver. Depending on the design of the cannula, each hose either serves one or both nostrils of the patient. The conserver likewise has two cannula hose ports. A sensing or pilot port is used exclusively for sensing the vacuum caused by patient inhalation. A slave or delivery port is used exclusively for delivery of oxygen to the patient.
When the patient inhales, oxygen is delivered by the delivery port through a delivery hose until inhalation ends. Because the two hoses of the cannula do not intermingle, the conserver is able to deliver oxygen the entire time the patient is inhaling. Therefore, dual-lumen conservers are commonly called “demand” conservers.
In a typical dual-lumen conserver (i.e., demand conserver), when the patient stops inhaling—causing the pilot diaphragm to close—the control chamber builds back to operating pressure (e.g., 22 PSI) almost immediately. Consequently, when the pilot diaphragm shuts against the pilot nozzle, flow to the patient stops. This is usually done by having a preset control flow between 100 cc and 350 cc per minute, depending on the design of the device. The need to stop flow as soon as the pilot diaphragm closes is because, in a demand conserver, the pilot diaphragm stays open as long as the patient inhales. The dual-lumen design of such conservers allows the unit to be sensitive enough to sense the vacuum caused by inhalation.
In comparison, a typical single-lumen conserver does not have that sensitivity. Single-lumen conservers use only a single cannula hose that serves both nostrils, which is coupled to a single port on the conserver. When no oxygen is flowing through the hose, the conserver can detect when the patient inhales, and oxygen delivery begins. However, once oxygen begins to flow through the hose, the flow of oxygen to the patient overwhelms the device's ability to sense the vacuum caused by the patient during inhalation and the device will no longer be able to sense when inhalation ends. Therefore, the device is constructed to stop the flow of oxygen after a predetermined amount of time, regardless of the patient's breathing pattern. There are some pneumatic devices that work this way, and all electronic devices work this way. These conservers are called “pulse” conservers, as they typically give a large pulse of oxygen and then shut themselves off and wait for the next breath.
Typically, dual-lumen conservers have the advantage of much better performance under all breathing conditions, meaning they deliver the correct amount of oxygen for the patient and work well with the widest variety of breathing patterns. Also, dual-lumen devices can have continuous or constant flow at all settings if required, whereas single-lumen devices typically have only a single continuous flow setting, such as a constant 2 liters per minute (LPM).
In comparison, single-lumen conservers have the advantages of a simpler (and less expensive) cannula hose, and because they only deliver a pulse of oxygen, these conservers can have a higher conservation ratio (many respiratory professionals believe that oxygen delivered at the end of inhalation is wasted because it does not get to the lungs before being exhaled). However, by controlling the rate of flow after the initial burst of oxygen, a dual-lumen device can be manufactured to conserve as much as a single lumen device.
One disadvantage of single-lumen pneumatic conservers is that they may be too quick to detect a breath after delivering oxygen. This problem is especially acute when the patient has a long breathing pattern (i.e. few breaths per minute). Because such a patient may still be inhaling on the same breath after oxygen is delivered, the patient may receive a “double pulse” or “multiple pulses” of oxygen for each breath. Electronic conservers generally avoid that problem by not registering a new inhalation until a specified period of time has elapsed since the last detection.
Furthermore, in typical prior art oxygen-conserving regulators, the inhaling patient receives an initial burst of oxygen from a bolus reservoir, often followed by a steady flow of oxygen at the regulator's flow rate while inhalation continues or until delivery is stopped. The initial burst volume of gas delivered to the patient at inspiration is equal to the volume of the reservoir multiplied by the pressure of the gas in the reservoir.
Some examples of oxygen-conserving regulators are described in U.S. Pat. Nos. 6,116,242 to Frye et al., 6,364,161 to Pryor, and 6,752,152 to Gale et al. Other embodiments are described in U.S. application Ser. No. 10/666,115 entitled “Differential Pressure Valve Employing Near-Balanced Pressure” by LeNoir E. Zaiser, which was filed on Sep. 19, 2003 (U.S. Publication No. 20040194829); U.S. application Ser. No. 10/706,872 entitled “Gas Conserving Regulator” by LeNoir E. Zaiser, et al., which was filed on Nov. 12, 2003 (U.S. Publication No. 20040154693); and U.S. application Ser. No. 10/772,220 entitled “Hybrid Electro-Pneumatic Conserver for Oxygen Conserving Regulator” by LeNoir E. Zaiser, et al., which was filed on Feb. 4, 2004 (U.S. Publication No. 20050039752). The teachings of those patents and applications are incorporated herein by reference in their entirety.